Thermal multiplier



2 Sheets-Sheet 1 J. SCHWARTZ THERMAL MULTIPLIER Nov. 30, 1954 Filed Oct. 14, 1952 Nov. 30, 1954 J. SCHWARTZ 2,695,967

THERMAL MULTIPLIER Filed Oct. 14, 1952 2 Sheets-Sheet 2 BY 52. 4 [KW I 34 a4 United States Patent THERMAL MULTIPLIER Joseph Schwartz, Teaneck, N. J., assignor to Avion Instrument Corporation, Paramus, N. J., a corporation of New York Application October 14, 1952, Serial No. 314,730

13 Claims. (Cl. 307149) My invention relates to an improved thermal multiplier and more particularly to an electrical means for multiplying and dividing voltages to obtain a voltaget proportional to the product or quotient of the amplitudes of any two given voltages.

In the prior art, voltages have been multiplied through servo-controlled potentiometers. Then too, it has been suggested to use a thermistor, controlled by a heater, connected in loop circuit together with a second thermistor also controlled by the heater and connected in a second circuit. Some devices according to this construction re quire the use of a load to bias the system in a given direction. None of the arrangements employing thermistors are able to go to zero or reverse polarity. Furthermore, thermistors are unstable devices.

One object of my invention is to provide a multiplier employing a bridge network which will accurately multiply two given voltages to produce a voltage representing their product.

Another object of my invention is to provide a multiplier which will accurately multiply voltages, which has no moving parts.

Another object of my invention is to provide a thermal multiplier for multiplying voltages in which the polarity of one or both of the voltages to be multiplied may be either positive or negative.

Another object of my invention is to provide a thermal multiplier which avoids the use of thermistors and which requires no load.

Other and further objects of my invention will appear from the following description.

In the accompanying drawings which form part of the instant specification and which are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views:

Figure 1 is a diagrammatic view of a thermal multiplier circuit containing one embodiment of my invention.

Figure 2 is a schematic view showing a thermal multiplier tube forming part of my thermal multiplier.

Figure 3 is a side elevation of the thermal multiplier tube shown schematically in Figure 2.

Figure 4 is a sectional view taken along the line 4-4 of Figure 3.

Figure 5 is an elevation Figure 3.

Figure 6 is an enlarged sectional View taken along the line 66 of Figure 3.

Referring now to Figure 3, the thermal multiplier tube, indicated generally by the reference numeral 10, comprises a housing 12 made of glass or other appropriate material, provided with a base 14, fitted with nine pins 16. The interior 18 of the housing 12 is evacuated to a vacuum sufficiently low to prevent loss of heat through gas convection, as for example, a vacuum of at least two microns or better. A pair of heat resistant support discs 20 and 22 formed of mica or the like are positioned within the tube and connected by a pair of support rods 24. The support discs carry a pair of sleeves 26 and 28 made of an appropriate heat resistant or heat conducting metal such as copper, silver, stainless steel or the like. Positioned within each sleeve 26 and 28, I lodge three separate filaments composed of fine tungsten wire (approximate 0. D. .005"). Each filament is four sleeve lengths long and is coated with aluminum oxide or other ceramic or heat resistant insulating material. The support rods 24 may be fitted with a handling member 30 by which the assembly may be positioned within the housing 12.

view along the line 5-5 of 2,695,957 Patented Nov. 30, 1954 The arrangement of the parts is such that the adjacent lengths of each filament are positioned in longitudinal proximity to each other within the sleeve, as can be seen by reference to Figure 6.

Referring now to Figure 2, it will be seen that the three filaments 32, 34 and 36 are positioned within the sleeve 28. The four lengths of the filament 32 are arranged as shown in Figure 6. The four lengths of filament 34 are positioned approximately as shown in Figure 6. Similarly, the four lengths of filament 36 are positioned adjacent to each other and in contact with portions of the other two filaments. Thus each filament contacts both of the other filaments through at least a portion of its length and contacts the wall of the sleeve. The three filaments 38, 40 and 42, which are lodged within the sleeve 26, are similarly connected. One end of filament 34 is connected to one end of filament 40 by conductor 44. Conductor 44 is connected to one of the terminal pins 16 of the base 14. One end of filament 36 is connected to one end of filament 42 by conductor 46, and this conductor is connected to one of the base pins. Similarly, one end of filament 32 is connected to one end of filament 38 by means of conductor 48 and this conductor is connected to another one of the base pins. This gives three base pins. The free ends of each of the six filaments are connected to a separate base pin as can be seen by reference to Figure 2, thus giving nine pins in all.

Referring now to Figure 1, resistors R1, R2 and R3 correspond to the filaments 38, 40 and 42. Similarly, the resistors Ri, Rz and R's correspond to the filaments 32, 34 and 36, housed within the other sleeve.

In the use of the tube, as will be pointed out more fully hereinafter, one of the filaments in each sleeve acts as a controller and the other two filaments within each sleeve act as the controlled resistors. Advantageously, I may make the filaments of tungsten, which will receive a ceramic coating. The arrangement is such that due to the close proximity of the resistor filaments within the sleeve, the temperature assumed by one of the controlled filaments within a sleeve will, by heat transferred from the heater filament directly by radiation and through the sleeve, be assumed by the other controlled filament so that both of the controlled elements of the assembly will arrive at the same temperature over a period of time. This time limit is made as short as possible by the construction just described whereby com paratively large areas for heat radiation and heat exchange are presented.

The thermal multiplier tube just described is connected in a circuit shown in Figure 1. It is desired to multiply voltage E1, impressed across the terminals 50 and 51, by a voltage E2, impressed across terminals 52 and 53, to obtain a voltage E0 across the terminals 54 and 56. A first bridge, indicated generally by the reference numeral 60, has no electrical connection with a second bridge, indicated generally by the reference numeral 62. The bridge comprises the resistors R2 and R'z connected in a Wheatstone bridge with resistors R4 and R5, the values of the resistors R4 and R5 being equal. A constant voltage E5 is impressed across the bridge input terminals 64 and 66. One output terminal 68 of the bridge is connected by conductor 70 to the input of the amplifier. The other output terminal 72 of the bridge is connected to the terminal 51. The terminal 50 is connected to the other side of the input to the amplifier 74. If we consider the output voltage of the bridge 60 as E4, the summation voltage of E1 and E4 represents the input to the amplifier 74. A constant voltage is impressed across the terminals 76 and 78 of the control network indicated generally by the reference numeral 80. The lengths of the filaments are such that R'1=R1, R2=R2 and R'3=R3. The bridge network 62 is completed by a pair of resistors Re and R: which are of equal resistance.

Let us now assume that E3 is the only voltage present. Due to the power developed, the temperature of the filament resistors within the sleeves are raised to a quiescent level. Now let us suppose an amplifier output EA is developed. This voltage is transformed through trans former 82 to a center tapped secondary winding 84. The voltage across resistor R1 will equal Es-l-Ea and the voltage developed across resistor R1 will equal E3"-EA- Thus R1 will assume a higher temperature due to the increased current flowing through the resistor R1 and resistor R1 will assume a lower temperature due to the reduced current flowing through it. Accordingly, the resistance R1 will be higher in value, depending upon its temperature coefiicient of resistance and the elevation of its temperature. R will assume a lower resistance, depending upon its temperature coefficient of resistance and the particular lower temperature reached by it. Since resistors R2 and R3 will be brought to the same temperature, which temperature is a function of the temperature of resistor R1, their resistances will respectively increase as the resistance R1 has increased. In a similar manner, the resistance Rz and R's will be decreased as the resistance R1 has decreased. Since the external resistances R4 and R5 are equal, the variation in resistance R2 with respect to R'z will unbalance bridge 60 so that its output voltage E4 will equal KE5 where the value of K is dependent upon the voltage EA. The external resistor Rs has a resistance equal to that of external resistor R7 in the bridge 62. Accordingly, this bridge will unbalance as the resistance of resistor R3 changes with respect to the resistance of resistor R's. Accordingly, the output voltage of bridge 62, E0, will equal KEz. Eliminating K from these equations, we get E1 across terminals 50 and 51. The amplifier will then develop a voltage EA of a magnitude such that in which Ke represents the error or difference between the input voltage E1 and the output voltage of the bridge 60. The gain of the amplifier 74 and the feed-back factor of the loop, however, is sufiiciently high such that E4 will be so small as to be negligible. In this manner, the bridge 60 automatically adjusts its unbalances by varying the resistance Rz with respect to Rz as a function of the input voltage E1 through the amplifier and the network 80 and my thermal multiplier tube.

Stated differently, the bridge 60 assumes such unbalance that its output voltage is a function of the input voltage applied across terminals 50 and 51. It will be seen that this result is achieved irrespective of the value of the constant voltage E5. If, for example, voltage E5 becomes greater, Ee will tend to become larger. This, however, varies the output of the amplifier in a direction such that the output of bridge 60 will seek the level of the voltage E1 or in a direction tending to reduce Ee to zero. In other words, the arrangement is such that the output of the amplifier acting through the network 80 and the thermal multiplier tube so adjusts the value of the resistance R2 with respect to the value of the resistance R1 as to reduce the error Ee to zero.

Since, as we have seen, E1 is equal to E4, we may substitute E1 for E4 in the equation for E above. Thus we obtain Since E is a constant, we have accomplished the multiplication desired. The output of bridge 62, E0, will be the product of the input voltage E1 multiplied by the multiplying voltage E2.

Owing to the arrangement of my invention just described, if no voltage is applied to the terminals 50 and 51, the bridge 60 will remain in balance with a Zero voltage output. In other words, both resistors R1 and R1 will be heated to the same temperature and hence resistors R2 and R'z will remain equal in value. Similarly, resistors R and R will remain equal in value. Accordingly, the output E0 of my multiplier will be zero. irrespective of what voltage is applied across terminals 52 and 53. In a similar manner the polarity of the voltage E1 will determine the polarity of the product together with the polarity of the voltage E2. If, for example, voltage E1 were of negative polarity, while voltage Ez were-of positive polarity, the change of value of the resistance of resistor R1 with respect to the value of the resistance of the resistor R1 would be in the opposite direction from that which would occur if E1 were of positive polarity. Stated diiferently, if the positive terminal of a voltage were applied to terminal 50, the bridge would be unbalanced in one direction. If a negative poten tial were applied to terminal 50, the bridge 60 would unbalance in the opposite direction. It will be seen, therefore, with my multiplier, the polarity of output voltage E0 can reverse and can go through zero. This is not possible with the voltage multiplying arrangements employing thermistors requiring a load.

By making resistors R1 and R1 equal to each other, resistors R and R's equal to each other, and resistors R3 and R's equal to each other, and making the controlled resistance elements subject to the same temperature conditions, a very accurate result can be obtained. Since the resistors are made out of the same material, they will behave similarly. The particular temperature coeflicients of resistance need not. be known. Sufiicient time, of course, must be allowed to permit a stable temperature condition to be reached. The construction of my thermal multiplier is such that this is reached in a comparatively short period of time. Extended heat-exchange surfaces are provided by employing resistors of small cross-sectional area and comparatively great lengths pressed closely adjacent each other and by making the sleeve tubes of heat resistant and heat conducting material. The two sleeves 26 and 28 are supported by heat insulating material so substantially no conduction between the sleeves takes place. The evacuated envelope in which the. sleeves are placed, prevents all passage of radiant heat energy from one sleeve to the other. Accordingly, each sleeve 26 and 28 will assume its own temperature, independent of the temperature of the other sleeve.

It will be seen that I have accomplished the objects of my invention. I have provided a multiplier employing a bridge network which will accurately multiply two given voltages to produce a voltage representing their product. I have provided a thermal multiplier'for multiplying voltages which has no moving parts and in which thepolarity of one or both of the voltages to be multiplied may be either positive or negative. I have provided a novel multiplier tube which is of especial use in my thermal multiplier. It will be further observed that by the simple expedient of keeping voltage E2 constant and varying the voltage E5, inverse multiplication and division can be readily performed, as will be apparent to those skilled in theart.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. It is therefore to be understood that my invention is not to be limited to the specific details shown and described.

Having thus described my invention, what I claim is:

1.. A thermal multiplier including in combination a first pair of resistors and a second pair of resistors connected in a Wheatstone bridge having a pair of input terminals and a pair of output terminals, thermal means for varying the resistance of one of the first pair of resistors with respect to the resistance of the other of the first pair of resistors in accordance with a first voltage, means for impressing a second voltage across the input terminals of the bridge and means for'removing a voltage representing the product of the first'and second volt ages from the output terminals of the bridge.

2. A thermal multiplier including in combination a first pair of resistors and a second pair of resistors connected in a Wheatstone bridge having a pair of input terminals and a pair of output terminals, thermal means for increasing the resistance of one of the first pair of resistors and for decreasing the resistance of the other of said first pair of resistors in accordance with a first voltage, means for impressing a second voltage across the input terminals of the bridge and means for removing a voltage representing the product of the first and second voltages from the output terminals of the bridge.

3. A thermal multiplier including in combination a first pair of resistors and a second pair of resistors connected in a Wheatstone bridge having a pair of input terminals and a pair of output terminals, thermal means for increasing the resistance of one of the first pair of resistors and for decreasing the resistance of the other of said first pair of resistors in accordance with a first voltage, means for impressing a second voltage across the input terminals of the bridge and means for removing a voltage representing the product of the first and second voltages from the ouput terminals of the bridge, the temperature coeificients of resistance of the resistors of the first pair and their resistances being equal and the rlesistances of the resistors of said second pair being equa 4. A thermal multiplier including in combination a first pair of resistors and a second pair of resistors connected in a Wheatstone bridge having a pair of input terminals and a pair of output terminals, a heating resistor, means for positioning one of the resistors of the first pair in heat-exchange relation with the heating resistor, means for heating the heating resistor in accordance with a first voltage whereby to unbalance the bridge agreeable thereto, means for impressing a second voltage across the input terminals of the bridge and means for removing a voltage representing the product of the first and second voltages from the output terminals of the bridge.

5. A thermal multiplier including in combination a first pair of resistors and a second pair of resistors connected in a Wheatstone bridge having a pair of input terminals and a pair of output terminals, the resistances and the thermal coefiicients of resistance of the resistors of the first pair being equal, the resistances of the resistors of the second pair being equal, a pair of heating resistors, means for positioning one of the resistors of the first pair in heat-exchange relation with one of the heating resistors, means for positioning the other resistor of the first pair in heat-exchange relation with the other of said heating resistors, means for heating said heating resistors, means agreeable to a first voltage for increasing the heating of the first heating resistor and for decreasing the heating of the second heating resistor whereby to unbalance the bridge in proportion to said first voltage, means for impressing a second voltage across the input terminals of the bridge and means for removing a voltage representing the product of the first and second voltages from the output terminals of the bridge.

6. A thermal multiplier including in combination a first pair of resistors and a second pair of resistors connected in a Wheatstone bridge having a pair of input and a pair of output terminals, a third pair of resistors and a fourth pair of resistors connected in a second Wheatstone bridge having a pair of input terminals and a pair of output terminals, a heating resistor, means for impressing a constant voltage across the input terminals of the second bridge, means for impressing the output voltage of the second bridge and a first voltage in series across the heating resistor, means for positioning one of the resistors of the first pair and one of the resistors of the third pair in heat-exchange relation with said heating resistor, whereby to unbalance the second bridge to bring its output voltage equal to the first voltage and opposite in sign and to unbalance the first bridge agreeable to the first voltage, means for impressing a second voltage across the input terminals of the first bridge and means for removing a voltage representing the product of the first and second voltages from the output terminals of the first bridge.

7. A thermal multiplier including in combination a first pair of resistors equal in resistance and having the same temperature coefiicient of resistance, a second pair of resistors equal in resistance connected in a Wheatstone bridge having a pair of input terminals and a pair of output terminals, a third pair of resistors equal in resistance and having the same temperature coefiicient of resistance and a fourth pair of resistors equal in resistance connected in a second Wheatstone bridge having a pair of input terminals and a pair of output terminals, means for impressing a constant voltage across the input terminals of the second bridge, a pair of heating resistors, means for impressing a second constant voltage across the pair of heating resistors whereby to raise their temperatures, means for impressing the output voltage of the second bridge and a first voltage across said heating resistors in push-pull relationship whereby to increase the temperature of one of said heating resistors and decrease the temperature of the other of said heating resistors, means for positioning one of the resistors of the first pair and one of the resistors of the third pair in heat-exchange relation with one of the heating resistors, means for positioning the other of the resistors of the first pair and the other of the resistors of the third pair in heat-exchange relation with the other of said heating resistors whereby to unbalance the second bridge to bring its output voltage to a value equal to the first voltage and opposite in sign and to unbalance the first bridge in proportion to the first voltage, means for impressing a second voltage across the input terminals of the first bridge and means for removing a voltage representing the product of the first and second voltages from the output terminals of the first bridge.

A thermal multiplier including in combination a multiplying bridge, a control bridge and a heating network, said multiplying bridge comprising a first pair of resistors having equal resistances and equal temperature coefficients of resistance and a second pair of resistors equal in resistance connected in a Wheatstone bridge having a pair of input terminals and a pair of output terminals, said control bridge comprising a third pair of resistors equal in resistance and having the same temperature coefiicient of resistance and a fourth pair of resistors equal in resistance connected in a second Wheatstone bridge having a pair of input terminals and a pair of output terminals, said heating network comprising a pair of heating resistors having equal resistances connected in a network with a center tapped secondary winding of a transformer having a primary winding, means for impressing a first constant voltage across the input terminals of the control bridge, means for impressing a second constant voltage across said heating resistors in parallel whereby to raise the temperature of said heating resistors, an amplifier having a pair of input terminals and a pair of output terminals, means for connecting the output of the amplifier across the primary winding of the transformer, means for impressing the output voltage of the control bridge and a first voltage in series across the input terminals of the amplifier whereby to increase the voltage across one of said heating resistors and decrease the voltage across the other of said heating resistors in proportion to said first voltage, means for positioning one of the resistances of the first pair and one of the resistances of the third pair in heat-exchange relation with one of the heating resistors, means for placing the other of the resistors of the first pair and the other of the resistors of the third pair in heat-exchange relation with the other of said heating resistors, the sign of the first constant voltage being such that the thermal unbalancing of the control bridge will be such that its output voltage will be equal to the first voltage and opposite in sign, means for impressing a second voltage across the input terminals of the multiplying bridge, the constuction being such that the multiplying bridge will be thermally unbalanced proportional to said first voltage, and means for removing a voltage representing the product of the first and second voltages vfrom the output terminals of the multiplying bridge.

9. A thermal multiplier tube including in combination a first resistor, a second resistor, means for positioning said resistors in heat-exchange relation with each other, means for electrically insulating the resistors from each other, means for applying a heating voltage across the first resistor and means for connecting the second re sistor in a thermal multiplier circuit.

10. A thermal multiplier tube including in combination a heat-conducting sleeve, a heating resistor positioned in said sleeve, a heated resistor positioned in said sleeve in heat-exchange relation with the heating resistor, means for electrically insulating the resistors from each other, means for applying a heating voltage across the heating resistor and means for connecting the heated resistor in a thermal multipiler circuit.

11. A thermal multiplier including in combination a heat-conducting sleeve, a heating resistor positioned in said sleeve, a pair of heated resistors positioned in said sleeve in heat-exchange relation with the heating resistor, means for electrically insulating the resistors from each other, means for applying a heating voltage across the heating resistor and means for connecting each of the pair of heated resistors in a thermal multiplier circuit.

12. A thermal multiplier including in combination an evacuated envelope, a first heat-conducting sleeve supported in said envelope, a second heat-conducting sleeve supported in said envelope and thermally insulated therefrom, a first heating resistor positioned in the first sleeve, a first heated resistor positioned in the first sleeve in heat-exchange relation with the first heating resistor, means for electrically insulating the first heating and 7 heated, resistors from each other, a second heating resistor positioned in the second sleeve, a second heated resistor-positioned in the second sleeve in heat-exchange relation with the second heating resistor, means for electrically insulating the second heating resistor from the second heated resistor, means for applying a heating voltage across the first heating resistor, means for applying a heating voltage across the second heating resistors and means for connecting the first and second heated resistors in a thermal multiplier circuit.

13. A thermal multiplier tube including in combination an evacuated envelope, a first heat conducting sleeve positioned in said envelope, a second heat-conducting sleeve positioned in said envelope and thermally insulated therefrom, a first heating resistor positioned in the first sleeve, a first pair of heated resistors positioned in the sleeve in heat-exchange relation with the first resistor, means for electrically insulating the first heating resistor and each; of the first pair of heated resistors from each other, a second heating resistor positioned in the second sleeve, a second pair of heated resistors positioned in the second sleeve in heat-exchange relation With the second heating resistor, means forelectrically insulating. the second heating resistor and each of said'second pair of heated resistors from each other, means for applying a heating voltage across said first heating resistor, means for applying a heaping voltage across the second heating resistor and means forconnecting said first and second pairs of heated resistors in a thermal multiplier circuit.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,577,111 Downing; et al. Dec. 4, 1951 2,596,992 Fleming May 20, 1952 

